stdlib: Fix LupvBoard to inherit from AbstractSystemBoard

In this patch:
https://gem5-review.googlesource.com/c/public/gem5/+/58909, the
AbstractBoard was refactored. While all otherboards were updated
correctly, the LupvBoard was not. This caused the nightly tests to
fail: https://jenkins.gem5.org/job/nightly/240

This patch corrects this issue.

Change-Id: Icac39d48358daf4acb2f7077f5d3e8871320812e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60095
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
1 file changed